Epidermal Growth Factor Receptor (also termed “EGFR”, “ErbB receptor”, or “ErbB1 receptor”) is a receptor protein tyrosine kinase which belongs to the ErbB receptor family. The ErbB receptor family includes ErbB (also known as ErbB1, or Her-1 receptor), ErbB2 (Her-2 receptor), ErbB3 (Her-3 receptor) and ErbB4 (Her-4 receptor), and other members of this family. Accordingly, the terms “ErbB1”, “ErbB1 receptor,” “ErbB receptor,” “epidermal growth factor receptor,” and “EGFR” are used interchangeably herein and refer to EGFR as disclosed, for example, in Carpenter et al. Ann. Rev. Biochem. 56:881-914 (1987), including naturally occurring mutant forms thereof (e.g., a deletion mutant EGFR as in Humphrey et al. PNAS (USA) 87:4207-4211 (1990)). It will be appreciated that as used herein, “EGFR” may be a native sequence EGFR or an amino acid sequence variant thereof.
EGFR generally comprises an extracellular domain, which may bind an ErbB ligand (such as EGF, TGF-α, etc.); a lipophilic transmembrane domain; a conserved intracellular tyrosine kinase domain; and a carboxyl-terminal signaling domain harboring several tyrosine residues which can be phosphorylated.
EGFR and its ligand, Epidermal Growth Factor (“EGF”) have been implicated in cellular proliferation and many types of cancers, including, human solid tumors. See e.g., Mendelsohn, Cancer Cell, 7:359 (1989); Mendelsohn, Cancer Biology 1:339-344 (1990), Modjtahedi and Dean Int'l, J. Oncology 4:277-296 (1994). This includes lung cancer, breast cancer, colorectal cancers, gastric cancer, brain cancer, cancer of the bladder, head and neck cancers, ovarian cancer, and prostate carcinomas. Modjtahedi and Dean, Intl J. Oncology 4:277-296 (1994).
A number of anti-EGFR antibodies are available commercially, or are currently in clinical development. Such antibodies include, but are not limited to, Vectibix® (panitumumab), Erbitux® (cetuximab); zalatumumab, nimotuzumab, and matuzumab.
Panitumumab (sold under the trade name Vectibix®), is a human, anti-EGFR monoclonal antibody approved for certain treatments of metastatic colorectal cancer (mCRC) in the U.S., Europe, Japan, and a number of other countries around the world. The nucleic and amino acid sequences for panitumumab are known, and can be found, inter alia, in U.S. Pat. Nos. 6,235,883 and 7,807,798 (Jakobovits et al.). The contents of these patents are hereby incorporated by reference in their entirety. The heavy chain (gamma) sequence of panitumumab is set forth in Seq Id No. 1, herein. The light chain (kappa) sequence of panitumumab is set forth in Seq Id No. 2, herein. As used herein, the term “AMG 954” refers to Vectibix® (panitumumab).
Isomerization of certain amino acid residues is an observed phenomenon in antibodies. For example, Wakankar et al. observed that certain aspartic acid residues (Asp) in the light chain Complementarity Determining Regions (CDRs) of two recombinant monoclonal antibodies were susceptible to such isomerization. Specifically, aspartic acid (Asp) isomerization in these antibodies led to formation of isoaspartate (IsoAsp), and the cyclic imide (Asu) variants of these antibodies. See Wakankar et al., Biochemistry, 2007 Feb. 13; 46(6):1534-44 (January 2007). The formation of these variants was found to reduce the binding affinities of these antibodies, thereby reducing their potency. Id.
Isomerization of certain amino acids has been observed with respect to Vectibix® (panitumumab). This isomerization appears to relate to certain losses in potency, as well as the possibility of chemical degradation, and is thus undesirable. There thus exists a strong desire to eliminate or reduce this isomerization.
As will be seen, the mutants described herein have (i) retained potency, or (ii) improved stability, or (iii) both.